Using temperature controllers and micro PLCs to speed small-scale automation projects
Improved PID PID control can be highly useful for temperature control applications. Power controllers like the G3ZA series of multi-channel controllers with fast-switching SSRs, together with temperature controllers using PID algorithms, can provide the fine- grained control needed to maintain the required temperature tolerances. Basic PID control involves a tradeoff between rapidly achieving the SV of operation with a measurable amount of overshoot or minimizing overshoot but with a slower ramp- up to the SV. In addition, there’s a tradeoff between achieving the SV and responding to disturbances in the actual PV as measured by a sensor. Better response to PV changes is often associated with poor SV ramp-up performance. To address those performance tradeoffs, Omron has developed an enhanced PID algorithm called 2-PID, or two degrees of freedom PID. The factory PID presets are suited for most heating applications and support responses with minimal overshooting. However, with 2-PID, designers can set the reaction speed to changes in the SV, and the controller automatically tunes the PID algorithm to provide an optimized response to disturbances in PV (Figure 3).
Figure 3: Omron 2-PID temperature control (bottom graph) combines good disturbance response (right side) with good step response (left side). (Image source: Omron)
2-PID control is included in Omron’s E5CC temperature controllers, like the E5CC- QX3A5M-003. These controllers can also implement basic on/ off control for less demanding applications. The large white PV display shows the PV and the smaller green SV display shows the desired value (Figure 4). The optional CX-Thermo management software supports fast programming. For simple applications, these controllers can implement timer functions and
basic logic operations with the intervention of a PLC. The RS-485 interface supports Modbus communication or Omron’s proprietary CompoWay/F. These controllers accept a variety of inputs, including:
■ 12 types of thermocouples
■ PT100 or JPt100 RTDs
■ 4 to 20 mA or 0 to 20 mA current inputs ■ 1 to 5 V, 0 to 5 V, or 0 to 10 V voltage inputs
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